Add olive oil to large cast-iron pan and bring to medium-high heat.
Sauté onions and garlic until slightly caramelized, about 15 seconds; add minced tomatoes and sauté for additional 30 seconds.
Add tomato paste and crushed red pepper and sauté for 30 seconds, then add chicken stock and simmer until reduced to 1/3 in volume, about 60 to 90 seconds.
Add heavy cream and bring to boil, then reduce to medium heat.
Add cooked orzo pasta, simmer until slightly thickened, about 1 minute, then stir in Parmesan and spinach, season to taste with salt and pepper, and fold in parsley.